The electroretinographic abnormalities in eyes with diabetic retinopathy will be determined, and the abnormalities will be related to pathologic changes in the fundus. Eyes with different degrees of severity of retinopathy will be studied. Panretinal fundus photography and fluorescein angiography will be used to grade the severity of retinopathy, with particular emphasis on grading the degree of retinal ischemia. The oscillatory potentials of the electroretinogram are wavelets found on the ascending limb of the b-wave. A reduction in the amplitude of the oscillatory potentials has been reported in eyes with nonproliferative diabetic retinopathy that are at high risk to develop proliferative retinopathy. A group of patients with non proliferative retinopathy will be evaluated with electroretinography, and followed for at least five years to test these previously reported findings.